GaryS62
Hi,

I have just finished constructing an 18 road marshalling yard for my layout, which includes 46 Cobalt IP Digital turnout motors.  I have tested all the track and point operations (using DCC) and all works fine.

I also want to operate the points using a control panel, and so I have constructed this using Cobalt Alpha Switch D boards and associated LED switches mounted in a mimic panel.  All point motors are wired to the 8 x Alpha Switches using 3 core cables, and the boards are daisy-chained together as recommended in the pack instructions.  I have checked the switch wiring several times and can detect no wiring problems between the points and the control panel, or within the control panel.

However, i have two problems which are making the control panel unusable.

The first is that since installing the point control panel, if it is turned off (not powered), I have some points (which are powered from the DCC bus) which are now switching intermittently and randomly.  I have done some on-line research and suspect this may be due to induced voltages in the cabling, some of which is up to 4m long, and have found a suggestion (probably from DCC Concepts) that fitting diodes in the switch wires at the points will eliminate this, and so have ordered some diodes to try this.

My second problem is more serious.  When I energise the control panel, I am getting a permanent track shorting fault.  My circuit breaker for the yard is set to trip at 5A and this is tripping constantly.

If I energise the control panel without the DCC track being powered, all the LED switches illuminate correctly and appear to switch correctly on the mimic panel.  But as soon as I switch on the DCC track power (which also powers the point motors), this is shorting out continually.

I assumed that the switch wiring in the IP digital turnout motors is electrically separate to the DCC track power and frog power circuits, so I am baffled why energising the Alpha Boards in the control panel is creating a short circuit in the track power supply, but can only assume this is through one or more of the point motors?

I have noticed during fault finding that the two left and right outputs from the Alpha Switch D are shorted to the common when switched in that direction - I have read in the instructions that the outputs should be open circuit and just a momentary switch, to actuate the point motors, but I have checked this also on another Alpha Switch D board which I haven't installed yet, and this is operating the same electrically.

is there a problem with my Alpha Switch D boards, are they not operating correctly, or could I have one or more rogue point motors?  Any help would be much appreciated.
Quote 0 0
AHJAY
One way or another we can sort this for you.

Its usually something not obvious and quite easy to remedy in the set-up.

It is far more likely that there is a wiring or configuration problem. If you have it working in basic terms but not when together, it is unlikely to be product problems... It will need some more depth of discussion so I will ask Mick, who is a "power user" of Alpha Switch on his exhibition layouts,  to pop into this thread and discuss.... so just a couple of comments here from me.

(1)  yes, long wires to switches will sometimes develop a capacitance/inductance that ccause problems with switching. A diode to common or two, one each to L and R should fix it.
(2)  Your random motor action definitely points to something associated with overall physical wiring layout. If it is not the switch wiring, a point motor cannot generate its own commands to move so there is something disturbing the dcc information to create this
(3)  The fact you have an issue in relation to tripping of a 5 amp breaker points to something related to other than panel. (By the way there is no point having a DCC circuit breaker if its set to the same level as the main system). Circuit breakers should always act before the main system.
(4)  Are you using a separated power supply for the Alpha Switch boards? wiring is not electrically separate if the power is shared.... Mick will discuss this

regards

Ahjay
Quote 1 0
GaryS62
Ahjay,

Many thanks for your quick response.

Picking up your points:

(1) Yes, having seen a previously posted note on this I have ordered diodes to install at the point motors on the right and left switching panel, which I am hopeful will cure the random switching of the IP digital point motors.
(2) I am quite confident that I don't have a wiring problem with the track and points, because I carried out a full sequence testing after installation of the track and points, before I had even installed the point switching wires, operating all 46 of the points via DCC.  I had no problems with points switching randomly, and certainly no short circuits on the track, before installing the control panel.  Even now, with the control panel not powered up, I am not getting any track short circuits.
(3) I have divided my layout into two separate sections, both separately powered.  The scenic side of the layout (which is complete, with track and points wired up and tested in DCC mode, and point switching wiring connected at the points and run to the control panel, although I've not built the scenic side control panel yet, so that isn't installed) is powered by an NCE Powerhouse Pro 5 Amp System and the marshalling yard is powered by an NCE Power Booster 5 Amp.  Both are electrically isolated but connected by the DCC bus.  I have also installed NCE EB-1 circuit breakers into each track power feed, and my intention is to reduce the trip current once I have completely finished wiring and testing the layout.
(4) The points control panel including the Alpha switch boards are powered by a separate mains fed 12V DC power supply.

As far as I can determine, there should be no physical wiring connection between the DCC track power and the control panel power supply, unless this is occurring inside a point motor.

With the control unit and Alpha switch boards de-energised, there are no stray voltages on the point switch wires, either DC or AC, that I can detect with my multimeter at the control panel.

When I have tested the resistance (with all power off) between the rails (DCC track) and the switch wire terminals in the control panel, each of the common wires are recording 0.7 Mega Ohms resistance to each rail and the two left and right switch wires are reading >9 Mega Ohms to each rail.  The measured resistance between the two rails is 1.15 Mega Ohms.  I am intending to fit DCC-BT2 bus suppressors to the non-supply end of each DCC bus, because my layout is 5.8m long, but haven't done this yet.

I am a little concerned about the difference between the insulation of the common switch wire, compared to the two switch wires, and I intend to carry out further detailed checks of all my wiring this coming weekend.  But I do have a 'spare' IP digital point motor (which doesn't throw over fully in one direction unless it is given a DCC command twice) and I have carried out continuity testing on this, and have measured 10.5 Mega Ohms between the two DCC inputs, around 5 Mega Ohms between any of the switch inputs, but only 1 Mega Ohm between the switch wire inputs and the DCC track power inputs.  So I suspect the difference is being caused by the Alpha switch panels, but will confirm this when I carry out detailed sequence testing.

Intuition tells me that there must be some kind of tracking path somewhere between the switch/control panel wiring and the DCC track wiring, to cause the short circuit tripping, but the way I have designed the power supplies and have wired up the track (individual red and black wiring for all DCC wiring. and separate 3 core cabling used for the point motor switching), there shouldn't even be anywhere where the wiring even runs that close together, but I am going to carry out full sequence testing at the weekend to hopefully eliminate (or identify) any such connection.

Not sure if any of this will help you to identify the potential problem, but once again, many thanks for your quick response.

Kind regards,

Gary
Quote 0 0
AHJAY
Hello Gary

Measurements in megohms are effectively not there electrically, so none of that is an issue... it is possible to measure at that level but not relevant to our discussions as both PCB layout (tracks + things just being alonside each other) and cable induction will be one of the reasons you see it. Anyway, at such tiny levels even room temperature and humidity wiould make a difference :-) :-).

SO - If troubleshooting for wrong connection decrease the sensitivity or range into k ohms areas..

long runs of adjacent wires will react as they effectively have a high capacitance, and with an active signal inside the wires it causes an inductive load that changes the impedance of the wire significantly - we get around it in some circumstances by plaiting 3 wires or twisting two - computer cable does it by both twisting wires and shielding each individual wire... Your solution would be the diodes which effectively de-couple things to reduce the problem.

Adding the terminators to the bus now would be a good idea. They also help in keeping the DCC clean.

I'd still reduce the protection in one section to less than 5 amps so the main units do not re-set. Stopping system resets is the only real benefit of having it in the first place, as the NCE booster already has a 5 amp oerload protector built in!

----------------------------------

Mick is looking at this thread and will comment or work with you to get it sorted.

regards... Ahjay
Quote 0 0
GaryS62
Hi Ahjay,

Thanks again for such a quick response.

my layout is installed in a well insulated garden building, with the temperature maintained to a minimum of 10 degrees C.  It does get much higher in the summer, usually tracking about 2 degrees under ambient temperature, but never below 10 degrees.

My DCC track wiring is based around a twisted bus cable (your DCDCW-TW25-3.5) with spurred hubs to which the dropper cables are connected, from each track length and point.  My point switching wiring is all 3-core 2183Y cable, which is twisted 0.5mm2 3-core cable, although these are gathered into cable looms back to the control panel, so there is certainly some potential for cable induction - although I didn't think these switch wires were energised unless a point is being switched?

I am expecting delivery of the diodes I've ordered shortly, so I may be able to install those early next week, and will fit the bus terminators at the same time - are these only necessary at the far end of the bus wire, or should I also fit one across the bus at the end it is fed from?

I will also reduce the circuit breaker trip current, even though I believe it is operating before the NCE booster protection is.

Thanks again and I will look forward to hearing from Mick.

kind regards,

Gary
Quote 0 0
Lee Edmondson Blueeighties
Hi Gary. Have you made any headway with your issues?

Regards,

Lee.
Regards,

Lee
Quote 0 0
GaryS62
Hi Lee,

Not really, no.

I have fitted diodes to all the switch wires, at the Cobalt IP Digital end, and this has cured the random switching of points that I was suffering.

I have also carried out a full check of wiring, both of the DCC wiring and switch wiring, and can find nowhere that the circuits come into contact with each other except possibly within the points motors.

I have now fitted a DCC Concepts bus terminator to my DCC bus open end (the other end being connected to the NEC Pro power booster via a circuit breaker and switch) and have reduced the NEC circuit breaker to 2.5A trip current.

i have further, this afternoon, carried out a full sequence test of every track and point in my 18 track marshalling yard, with a DCC sound fitted loco, switching the points using DCC commands from the NEC Pro handset, and with the point control panel unpowered, everything works as it should. No stalls, no track short circuits, no circuit breaker trips, nothing.

However, as soon as I apply power to the point control panel I have built, the circuit breaker keeps tripping repeatedly.

I built the control panel using 8 Alpha D switch cards, and these are daisy-chained together (for 12V power). I had time this afternoon to separate all the interconnecting power leads, and decided to power up each Alpha D card separately.

in each and every case, all 8 powered up individually, without the circuit breaker tripping, and I was able to switch the relevantly powered switches on the control panel to operate the relevant points correctly.

However, as soon as I connected more than two of the two of the Alpha D cards to the 12V supply, the DCC circuit breaker tripped.

I am thus completely puzzled. Even if there is a fault on one or more of the Alpha D boards, I don’t understand why powering up the Alpha D boards would cause the track DCC to trip, because they are completely independently powered circuits, and apart from both connecting to each point motor, don’t come into contact with each other.

I have included photos of my marshalling yard, point control panel and the wiring of the Alpha D control panels for context.

Any suggestions would be most welcome.

Kind regards,

Gary D1C0CE55-908D-49D0-B126-EABD053FD55F.jpeg  A5AEE806-6639-4098-81FF-BEA755B1D470.jpeg  97B590CE-315A-4D38-A19B-72ED462BCAAC.jpeg 
Quote 0 0
AHJAY
Nice tidy wiring!

It is not a fault in the Alpha-D boards, but it IS a symptom of an overly sensitive overload protector in the power supply structure.

There is always a larger load at the moment of turn-on than a few milliseconds later, and an overly fast reaction on the power supply will make it trip.

A simple test: Try something simple like...

* having a switch so that you turn on the panels etc AFTER you turn on the power supply, therefore letting the power supply stabilise before adding a load.

* Adding an incandescent 12v bulb in series with one wire. A car tail light bulb (or two in series) this is an inductive load that is relatively "Slow" so it will also buffer the initial turn-on load and give the power supply time to stabilise... but should do nothing else (not even light less the load is high)

regards, Ahjay
Quote 0 0
GaryS62
Thanks Ahjay,

You’ve read my mind!!

I deduced yesterday that the EB1 circuit breaker trips were current related rather than due to a short circuit, and after connecting my meter in series to measure current I found that there is a significant current drawn, up to 6.5A, when I switch on the point control panel.

It seems that the 8 Alpha boards all send a signal to the point motors at switch on, so that all 46 point motors attempt to change even when set to the correct position, drawing excess current.

I have found that a similar thing happens if I turn on the track power after energising the panel, because that also seems to have the same effect on the point motors.

I essence, what I was experiencing is that each time the EB1 trips, and resets, power is reapplied to the points and this causes the transient peak current that then trips the EB1 again, and this continues as a trip-reset-trip cycle.

I have tested the system with the EB1 bridged out and everything works fine.  The NEC 5A booster seems to tolerate the transient start up current and doesn’t trip.

I’ve got two EB1s and I’ve tested them both, and both trip exactly the same.

I have seen in the EB1 instructions that it is possible to change CV values to increase the trip sensitivity time to 500mS.

I’m not sure that will be long enough, because the peak current appears on my meter for around one second, but that may be hysteresis in the meter, so could be worth a try.

Otherwise I may have to fit a switch to bypass the EB1 when I power up the point control panel, to see if that works, or to simply live without the additional protection of the circuit breakers and to rely on the power supplies to deal with a short circuit.

At least this exhonerates my wiring, which vindicates my belief that this wasn’t a short between the 13V dc and track DCC voltage, but it is a surprise that the point motors draw current, even momentarily, when energised if they are already in the selected position, but this is my first experience of using the IP Digital points and DCC, so I guess there are a few lessons to learn on the journey.

Many thanks for your support and advice.

Kind regards,

Gary

Quote 0 0
AHJAY
I am guessing 500mS will do it.

It is not really the point motors but the control devices... All of them have power filtering of one kind or another using capacitors for filters. It's just the initial surge as many electrolytic caps all charge at once... and they do charge quote fast.

regards, Ahjay
Quote 0 0
GaryS62
Thanks Ahjay,

I’ll try that and see if it does help.

Many thanks

Gary
Quote 0 0